The word Dvandva in Sanskrit has meaning such as – a pair or a couple of animals, men, etc., and opposite situations or qualities such as, heat and cold, pleasure and pain, hard and soft, and so on.
The word, Dvandva, has assumed importance in spiritual discipline because one must strive for overcoming the vicissitudes of life and learn to remain unaffected by the impact of the opposites like pleasure and pain, success and failure, loss and gain.
The word Dvandva also means doubt, uncertainty, fight or duel.
The word ‘dvandvatia’ has appeared in the Bhagavad Gita (IV.22) to denote a person who is beyond the dichotomies, remains firm, unaffected and unperturbed in the vastly changing situations in daily life.
In the 15th chapter of the Bhagavad Gita, Bhagavan Sri Krishna declares that those who become free from the opposites like joy and sorrow reach the ultimate absolute state of bliss (XV.5), from which there is no return to the world of life and death.
In Yogasutra of Patanjali, the chief commentator Vyasa has pointed out, in his commentary of verse II.32, that of the five niyamas or observances, the third one, called tapas (austerities) means cultivating the habit of mortification or dvandvasahanam (bearing of extremes). This is said to lead to yogic powers of the body and sense organs (Yogasutra: II.43).
The examples of dvandvas mentioned by Sage Vyasa are – hunger and thirst, heat and cold, standing and sitting, and silence of two types – kastha mauna (stock stillness) and akara mauna (formal stillness).
Since all the members are syntactically connected in the dvandva compound, Sri Krishna declares that he is dvandva among compounds (Bhagavad Gita Chapter X – 33).
Source - Notes taken from Encyclopedia of Hinduism Volume III - page 566 - IHRF - Rupa - 2011